refactor: git repo and relative path handling (#38522)

1. simplify "StorageRepo" code
2. simplify git.OpenRepository code
3. by the way, clean up some unused files in git test fixtures.

modules/git/gitcmd/repo.go

@@ -10,7 +10,14 @@ import (
 )
 
 type RepositoryFacade interface {
-	GitRepoUniqueID() string
+	// GitRepoManagedID returns a "managed id", which should be a cache-key-friendly string.
+	// e.g.: ID with prefix&suffix or UUID
+	GitRepoManagedID() string
+
+	// GitRepoLocation returns the location for the git repository.
+	// * relative path: will be converted to an absolute path by setting.RepoRootPath
+	// * absolute path: will be used as-is
+	// * in the future: maybe URI for more flexible definitions
 	GitRepoLocation() string
 }
 
@@ -26,3 +33,34 @@ func RepoLocalPath(repo RepositoryFacade) string {
 	}
 	return filepath.Join(setting.RepoRootPath, filepath.FromSlash(repoLoc))
 }
+
+type repositoryUnmanaged string
+
+func (r repositoryUnmanaged) GitRepoManagedID() string {
+	panic("this repo is not managed by Gitea, can't be used in this managed context")
+}
+
+func (r repositoryUnmanaged) GitRepoLocation() string {
+	return string(r)
+}
+
+func RepositoryUnmanaged(s string) RepositoryFacade {
+	return repositoryUnmanaged(s)
+}
+
+type repositoryManaged struct {
+	id  string
+	loc string
+}
+
+func (r *repositoryManaged) GitRepoManagedID() string {
+	return r.id
+}
+
+func (r *repositoryManaged) GitRepoLocation() string {
+	return r.loc
+}
+
+func RepositoryManaged(id, loc string) RepositoryFacade {
+	return &repositoryManaged{id, loc}
+}